For example, for car batteries, it can be significantly improved by adding this attachment - an automatic device that turns it on when the voltage on the battery drops to a minimum and turns it off after charging. This is especially true when storing the battery for a long time without operation - to prevent self-discharge. The diagram of the console is shown in the figure below.

The maximum voltage for car batteries is within 14.2...14.5 V. The minimum permissible during discharge is 10.8 V. After connecting the battery and turning on the network, press the SB1 “Start” button. Transistors VT1 and VT2 close, opening the key VT3, VT4, which turns on relay K1. With its normally closed contacts K1.2, it turns off relay K2, the normally closed contacts of which (K2.1), when closed, connect the charger to the network. Such a complex switching scheme is used for two reasons: firstly, it ensures decoupling of the high-voltage circuit from the low-voltage one; secondly, so that relay K2 turns on at the maximum battery voltage and turns off at the minimum, because The RES22 relay used has a switching voltage of 12 V.

Contacts K1.1 of relay K1 switch to the lower position according to the diagram. During the battery charging process, the voltage across resistors R1 and R2 increases, and when the unlocking voltage is reached at the base of VT1, transistors VT1 and VT2 open, closing the key VT3, VT4. Relay K1 turns off, including K2. The normally closed contacts K2.1 open and de-energize the charger. Contacts K1.1 move to the top position according to the diagram. Now the voltage at the base of the composite transistor VT1, VT2 is determined by the voltage drop across resistors R1 and R2. As the battery discharges, the voltage at the base of VT1 decreases, and at some point VT1, VT2 close, opening the key VT3, VT4. The charging cycle begins again. Capacitor C1 serves to eliminate interference from the bounce of contacts K1.1 at the time of switching.

The device is adjusted without a battery or charger. An adjustable constant voltage source with regulation limits of 10...20 V is required. It is connected to the circuit terminals instead of GB1. The resistor R1 slider is moved to the upper position, and the R5 slider is moved to the lower position. The source voltage is set equal to the minimum battery voltage (11.5...12 V). By moving the R5 engine, relay K1 and LED VD7 are turned on. Then, raising the source voltage to 14.2...14.5 V, moving the R1 slider turns off K1 and the LED. By changing the source voltage in both directions, make sure that the device turns on at a voltage of 11.5...12 V, and turns off at 14.2...14.5 V. The photo shows a homemade charger for car batteries, with a built-in prefix.

The article discusses the circuit of a simple device, by adding it to your charger (charger), the charging process can be automated. It will also help keep your battery charged during long-term storage, which will significantly increase its service life.

The device is an electronic relay that monitors the voltage of the connected battery. The relay has two response thresholds based on the highest and lowest voltage values, set during the commissioning process.

Contact group K1.1 is connected to the break in one of the wires going to the terminal block for connecting the battery. The device is also powered from this terminal block.

Device setup. To configure the node, you will need a power source with an adjustable voltage value. We supply power to input XS1 (Fig. 1). We install the slider of resistor R 2 in the upper position according to the diagram, and R3 in the lower position. We set the voltage value to 14.5 V. In this case, transistor VT 2 must be closed, and relay K1 must be de-energized. By adjusting R 3, we achieve the activation of relay K1. Now we set the voltage to 12.9 V, and by adjusting R 2 we turn off K1.

Since the contacts of relay K1.2, in the off state, bypass resistor R2, the activation and shutdown settings of K1 are independent of each other.

About the details of the device. Trimmer resistors R 2, R 3, type SP-5, precision zener diode D818 can be replaced with two back-to-back D814 with similar voltage stabilization values. Relay K1 with a supply voltage of 12 V, with two groups of normally closed contacts. Contact group K1.1 must be designed for the battery charging current.

Having supplemented the charger at your disposal for a car battery with the proposed automatic device, you can be calm about the battery charging mode - as soon as the voltage at its terminals reaches (14.5 ± 0.2) V, charging will stop. When the voltage drops to 12.8..13 V, charging will resume.

The attachment can be made as a separate unit or built into the charger. In any case, a necessary condition for its operation will be the presence of a pulsating voltage at the output of the charger. This voltage is obtained, say, when installing a full-wave rectifier in the device without a smoothing capacitor.

Scheme of the set-top box

It consists of a thyristor VS1, a control unit for thyristor A1, a circuit breaker SA1 and two indication circuits on LEDs HL1 and HL2. The first circuit indicates the charging mode, the second circuit controls the reliability of connecting the battery to the terminals of the machine.

If the charger has a dial indicator - an ammeter, the first indication circuit is not necessary.

The control unit contains a trigger on transistors VT2, VTZ and a current amplifier on transistor VT1. The base of the transistor VTZ is connected to the engine of the tuning resistor R9, which sets the switching threshold of the trigger, i.e. the switching voltage of the charging current. The switching “hysteresis” (the difference between the upper and lower switching thresholds) depends mainly on the resistor R7 and with the resistance indicated on the diagram it is about 1.5 V.

The trigger is connected to conductors connected to the terminals of the battery and switches depending on the voltage on them.

Rice. I. Schematic diagram of the machine attachment.

Transistor VT1 is connected by a base circuit to the trigger and operates in electronic key mode. The collector circuit of the transistor is connected through resistors R2, R3 and the control electrode section - the cathode of the SCR with the negative terminal of the charger. Thus, the base and collector circuits of transistor pa VT1 are powered from different sources: the base circuit from the battery, and the collector circuit from the charger.

SCR VS1 acts as a switching element. Using it instead of the contacts of an electromagnetic relay, which is sometimes used in these cases, provides a large number of switches on and off of the charging current necessary to recharge the cumulative battery during long-term storage.

As can be seen from the diagram, the SCR is connected by the cathode to the negative wire of the charger, and by the anode to the negative terminal of the battery. With this option, the control of the thyristor is simplified: when the instantaneous value of the pulsating Voltage at the output of the charger increases, current immediately begins to flow through the control electrode of the thyristor (if, of course, transistor VT1 is open).

And when a positive (relative to the cathode) voltage appears at the anode of the thyristor, the thyristor will be reliably open. In addition, such inclusion is advantageous in that the SCR can be attached directly to the metal body of the machine or the charger body (if the console is placed inside it) as a heat sink.

You can turn off the set-top box using switch SA1 by placing it in the “Manual” position. Then the contacts of the switch will be closed, and through “resistor R2 the control electrode of the thyristor will be” connected directly to the terminals of the charger.” This mode is needed, for example, to quickly charge the battery before installing it in a car.

Details and design

Transistor VT1 can be the series indicated on the diagram with letter indices A - G; VG2 and VT3 - KT603A - KT603G; diode VD1 - any of the D219, D220 series or other silicon; Zener diode VD2 - D814A, D814B, D808, D809; SCR - KU202 series with letter indices G, E, I, L, N, as well as D238G, D238E; LEDs - any of the AL 102, AL307 series (limiting resistors R1 and R11 set the desired forward current of the LEDs used).

Fixed resistors - MLT-2 (R2), MLT-1 (R6), MLT-0.5 (Rl, R3, R8, R11), MLT-0.25 (others). Trimmer resistor R9 is SP5-16B, but another one with a resistance of 330 Ohm... 1.5 kOhm will do.

If the resistance of the resistor is greater than that indicated in the diagram, a constant resistor of such resistance is connected parallel to its terminals so that the total resistance is 330 Ohms.

The parts of the control unit are mounted on a board (Fig. 2) made of one-sided foil fiberglass laminate with a thickness of 1.5 mm. The tuning resistor is fixed in a hole with a diameter of 5.2 mm so that its axis protrudes from the printing side.

The board is mounted inside a case of suitable dimensions or, as mentioned above, inside the charger case, but always as far as possible from heating parts (rectifier diodes, transformer, SCR). In any case, a hole is drilled in the housing wall opposite the SS trimmer. LEDs and switch SA1 are mounted on the front wall of the case.

Rice. 2. Printed circuit board of the machine.

To install an SCR, you can make a heat sink with a total area of ​​about 200 cm2. For example, a duralumin plate with a thickness of 3 mm and dimensions of 100X100 mm is suitable. The heat sink is attached to one of the walls of the case (say, the back) at a distance of about 10 mm - to ensure air convection.

It is also possible to attach the heat sink to the outside of the wall by cutting a hole in the housing for the thyristor.

Before attaching the control unit, you need to check it and determine the position of the trimmer resistor motor. A DC rectifier with an adjustable output voltage of up to 15 V is connected to points 1 and 2 of the board, and the indication circuit (resistor R1 and LED HL1) is connected to points 2 and 5. The trimmer resistor motor is set to the lowest position according to the diagram and voltage is supplied to the control unit about 13 V. The LED should light up. By moving the trimmer resistor slider up in the circuit, the LED goes out. Smoothly increasing the supply voltage of the control unit to 15 V and decreasing to 12 V, use a trimming resistor to ensure that the LED lights up at a voltage of 12.8...13 V and goes out at 14.2...14.7 V.

A. Korobkov.

Korobkov Alexander Vasilievich- leading specialist at one of the Moscow enterprises, born in 1986. He took up amateur radio at school, where he assembled a detector receiver as an eighth-grader. Two years later I mastered superheterodyne. In the 60s he developed and assembled a transistor tape recorder. The first publications in the magazine “Radio” date back to the same period. A little later he began to publish in the VRL collection. The main topic of publications in the last decade has been automotive electronics.

This device is connected as a set-top box to a charger, a variety of schemes of which have already been described on the Internet. It displays on the liquid crystal display the input voltage value, the amount of battery charging current, charging time and charging current capacity (which can be either in Amp-hours or milliamp-hours - depends only on the controller firmware and the shunt used). The output voltage of the charger should not be less than 7 volts, otherwise this set-top box will require a separate power source. The device is based on a PIC16F676 microcontroller and a 2-line liquid crystal indicator SC 1602 ASLB-XH-HS-G. The maximum charging capacity is 5500 mA/h and 95.0 A/h respectively.

The schematic diagram is shown in Fig. 1.

Connection to the charger - see Fig. 2.

When turned on, the microcontroller first requests the required charging capacity. Set by button SB1. Reset - button SB2.

If the button is not pressed for more than 5 seconds, the controller automatically switches to measurement mode. Pin 2 (RA5) is set high.

The algorithm for calculating the capacity in this set-top box is as follows:

Once a second, the microcontroller measures the voltage at the input of the set-top box and the current, and if the current value is greater than the least significant digit, it increases the seconds counter by 1. Thus, the clock only shows the charging time.

Next, the microcontroller calculates the average current per minute. To do this, the readings of the charger are divided by 60. The whole number is recorded in the meter, and the remainder of the division is then added to the next measured current value, and only then this sum is divided by 60. Having thus made 60 measurements in the meter, the number of the average value will be current per minute.

Next, the average current value is in turn divided by 60 (using the same algorithm). Thus, the capacitance counter increases once per minute by one sixtieth of the average current per minute.

After this, the average current counter is reset to zero and counting starts over. Each time, after calculating the charging capacity, a comparison is made between the measured capacity and the specified one, and if they are equal, the message “Charging complete” is displayed on the display, and in the second line - the value of this charging capacity and voltage. A low level appears at pin 2 of the microcontroller (RA5), which leads to the LED extinguishing. This signal can be used to turn on a relay, which, for example, disconnects the charger from the network (see Fig. 3).

Setting up the device comes down to setting the correct readings of the charging current (R1 R3) and input voltage (R2) using a reference ammeter and voltmeter. To accurately set the set-top box readings, it is recommended to use multi-turn trimmer resistors or install additional resistors in series with the trimmers (select experimentally).

Now about shunts.

For a charger with a current of up to 1000 mA, you can use a 15 V power supply, a 5-10 Ohm resistor with a power of 5 W as a shunt, and in series with the battery being charged a variable resistance of 20-100 Ohms, which will set the charging current.

For a charging current of up to 10 A (max 25.5 A), you will need to make a shunt from high-resistance wire of a suitable cross-section with a resistance of 0.1 Ohm. Tests have shown that even with a signal from the current shunt equal to 0.1 volts, the tuning resistors R1 and R3 can easily set the current reading to 10 A. However, the larger the signal from the current sensor, the easier it is to set the correct readings.

As a shunt for a 10 A set-top box, I tried to use a piece of aluminum wire with a cross-section of 1.5 mm and a length of 30 cm - it works great.

Due to the simplicity of the circuit, a printed circuit board for this device was not developed; it is assembled on a breadboard of the same dimensions as the liquid crystal indicator and is fixed at the back. The microcontroller is installed on the socket and allows you to quickly change the firmware to switch to a different charger current.